The present invention relates to compact fluorescent lamp systems. It finds particular application in conjunction with starting compact fluorescent lamp systems having high frequency electronic ballast units and will be described with particular reference thereto. It will be appreciated, however, that the invention will also find application in starting other lamp systems.
Many compact fluorescent lamp systems include a sealed, gas-filled lamp having multiple fingers. A gas filling of Argon at approximately 3 Torr coupled with a sufficient quantity of mercury, for example, is commonly used. An inner wall of the lamp is coated with a material (e.g., a mixture of phosphors) which fluoresces when it is excited by ultra-violet radiation generated by the ionized mercury vapor.
The fingers of a compact fluorescent lamp are typically formed from several shaped tubes. Bridges (i.e., passageways) connect all but two ends of adjacent tubes thereby forming a lamp having a hexagonal-shaped or octagonal-shaped geometry. Lamp electrodes are sealed into the unconnected adjacent ends. Each lamp electrode provides an electrical path into the lamp. Input connection leads from a high-frequency ballast unit are secured to the lamp electrodes.
When a starting voltage is delivered from the ballast unit to the conducting electrodes, that voltage is transferred into the discharge space of the lamp via the lamp electrodes. The starting voltage creates electromagnetic fields within the lamp which create a breakdown voltage path and a current within the tubes. The voltage potential within the tubes breaks-down (i.e., ionizes) the gas. Once the mercury atoms are ionized, and a threshold number of ions are produced, the lamp will start and the coating material within the lamp begins to fluoresce.
In its initial state, the gas within the lamp presents a high impedance to the ballast. Therefore, the starting voltage supplied by the ballast must be high enough to overcome this impedance and create an ionized gas capable of supplying the necessary current to operate the lamp. Supplying a starting voltage capable of ionizing enough gas to start the lamp, however, can produce an undesirable side-effect. More specifically, if the two lamp electrodes are in close proximity to one another, a higher starting voltage may occur due to a capacitive breakdown path between the tubes containing the lamp electrodes. When this occurs, not enough discharge current travels within the lamp tubes to start the lamp. These capacitive breakdown paths between the lamp electrodes most often occur when high frequency (e.g., greater than 20 kHz) electronic ballast units are used to control the power supplied to the lamp.
One way to start the compact fluorescent lamp when capacitive displacement current exists between the lamp electrodes is to increase the starting voltage delivered by the ballast unit. Although the displacement current created by the increased starting voltage still exists between the lamp electrodes, more discharge current travels through the lamp tube, thereby permitting the ionized gas to start the lamp. Supplying higher starting voltages to the lamp assembly, however, is undesirable for various reasons. For example, these higher voltages may cause additional voltage stresses on the ballast components which, in turn, require more expensive components to withstand these higher starting voltage requirements.
The present invention provides a new and improved apparatus and method which overcomes the above-referenced problems and others.